1. Field of the Invention
The object of the invention is a method of producing high-molecular weight polyphenylene oxide (PPO) by the oxidative coupling of a diortho-substituted phenol in the presence of a copper-amine catalyst complex; an activator of a polyvalent alcohol, and an alkali compound; and, optionally, the hydrobromide of a secondary amine.
2. Description of the Prior Art
PPO and methods of producing it are known. Such methods are described, for example, in Buhler, "Spezialplaste," Akademieverlag, Berlin, 1978 as well as in U.S. Pat. Nos. 3,306,874 and 3,306,875 and in DE-AS 22 17 161.
However, the methods in which diortho-substituted phenols are oxidatively coupled in the presence of oxygen by a copper amine complex have prevailed in industry.
High PPO molecular weights can be achieved with the method of DE-OS 24 46 425. Nevertheless, this method is avoided in practice, because the work must be performed at very high pressures. This involves considerable extra expense for equipment and safety measures.
French Patent No. 1,440,527 describes a method for making PPO by emulsion polymerization in which a combination of oleinic acid and triethanol amine is used, among others, as an emulsion agent.
The method of U.S. Pat. No. 335,257 for producing PPO by the oxidation of 2,6-dimethyl phenol with oxygen utilizes a catalyst containing metallic copper, a salt of bivalent copper, methanol and an amine.
DE-OS describes a method of producing PPO in which phenols are treated with oxygen in the presence of a copper amine complex and metal bromide. While an accelerating effect was demonstrated for alkali and alkaline earth bromides, non-metallic bromides, e.g. ammonium bromide, do not appear to show such acceleration.
A catalyst is used in Japanese Patent No. Sho-48-32793 which consists of:
1. a copper (I) salt,
2. a compound of an alkali or alkaline earth element which reacts in an alkaline manner, such as, lithium carbonate, sodium hydroxide or potassium acetate, and
3. a nitrile, e.g. propionitrile or phthalodinitrile. The oxidation occurs with oxygen or a mixture of oxygen and air in a 1:1 ratio.
However, previous methods are not satisfactory in practice. Oxygen is usually required as an oxidizing agent. In addition to the greater expense associated with the use of oxygen as compared to air, for example, the use of pure oxygen also involves a greater safety risk. Benzene of a solvent containing chlorine, such as, trichloroethylene is frequently used. However, these solvents should be avoided due to their suspected carcinogenic nature.
The reaction time should be under two hours in order to assure that the procedure is economical. Also, if the reaction time is longer, by-products can easily develop which add a disturbing discoloration to the reaction mixture.
Finally, a high degree of polymerization is also important. A degree of polymerization of 100 is required for manufacturing threads, fibers, coatings and other products (see DE Patent 20 12 443), and a degree of polymerization of 250 is desirable, so that a subsequent molding deformation is completely assured. This corresponds to a J-value of 50, that is, the relative viscosity change of a 0.5% solution of the reaction product in chloroform at 25.degree. C. in relation to the concentration is over 50 ml/g.
Thus, a need continues to exist for a process which produces high-molecular weight PPO in a short reaction time, without having to use pure oxygen as an oxidizing agent, and with minimal risk to safety.